`hermes update` ran the webui build with `capture_output=True` and no timeout. On low-memory hosts (WSL2's 4 GB default, small VPSes, antivirus stalls) Vite goes silent for minutes; users see a frozen terminal, decide the update is hung, and reboot. The reboot lands *after* `pip install -e .` has already touched the install but *before* the build completes, leaving the `hermes` launcher in place while `hermes_cli` is no longer importable — i.e. `ModuleNotFoundError: No module named 'hermes_cli'` (#33788, same class as #32384).
Changes:
- New `_run_with_idle_timeout()` helper: streams subprocess output line-by-line (so the user sees Vite progress in real time) and kills the process if no bytes appear on stdout/stderr for 180s. The existing stale-dist fallback (#23817) then serves the previous build instead of failing the update.
- `_build_web_ui()` uses the helper for `npm run build` (the actual stall site). `npm install` keeps `subprocess.run` + capture_output to preserve the existing EPERM-retry-on-Windows contract.
- Both `cmd_update` call sites print `→ Core update complete. Building dashboard (optional)...` before the webui build. The CLI is fully functional at this point; a webui-build failure only affects `hermes dashboard`. Telegraphing the boundary explicitly stops users from rebooting through the build step.
Tests:
- `tests/hermes_cli/test_run_with_idle_timeout.py` — 4 tests covering streaming success, nonzero exit, idle-kill, and missing-binary cases. Uses real `subprocess.Popen` on tiny Python scripts; isolated in its own file so per-file canonical-runner parallelism doesn't pair it with the mock-heavy tests.
- `tests/hermes_cli/test_web_ui_build.py` — updated existing tests to patch `_run_with_idle_timeout` for the build step in addition to `subprocess.run` for the install step.
- `tests/hermes_cli/test_cmd_update.py::test_update_refreshes_repo_and_tui_node_dependencies` — same update.
Full suite: `scripts/run_tests.sh tests/hermes_cli/` → 5646 passed, 0 failed.
Fixes#33788.
Follow-up to PR #23824. Adds two correctness fixes on top of the
contributor's salvaged commit:
1. Stale-dist fallback no longer gated on `fatal=False`. `cmd_dashboard`
passes `fatal=True` and is the primary scenario this fallback is for
(issue #23817 — Windows Scheduled Task at logon). The previous gate
meant the fallback never fired in the case it was designed for.
2. `--skip-build` now verifies the dist actually exists before starting
the server. Without this, a misconfigured pre-build would launch the
dashboard pointing at a missing dist and silently serve 404s. We now
exit 1 with a clear "pre-build first: cd web && npm run build"
message, and on success print which dist directory is being used.
Verified end-to-end on Linux:
- build fails + stale dist (fatal=True) -> fallback fires
- build fails + no dist (fatal=True) -> exit 1 with stderr surfaced
- build fails + stale dist (fatal=False) -> fallback fires
- --skip-build + missing dist -> exit 1 with clear guidance
- --skip-build + valid dist -> 'Skipping web UI build...'
On Windows systems using a Chinese GBK locale, `hermes update` could misreport the Web UI build as failed even when `npm run build` actually succeeded. The failure was caused by Python decoding captured npm output with the process locale inside a background subprocess reader thread. When npm emitted bytes such as `0x85`, decoding under GBK raised `UnicodeDecodeError`, and Hermes then surfaced a misleading "Web UI build failed" warning.
This change makes the npm install/npm ci path and the Web UI build step decode captured output explicitly as UTF-8 with `errors="replace"`. That keeps unexpected bytes from crashing output collection, preserves successful builds, and prevents false negatives during update on Windows.
The patch also adds regression tests that verify these subprocess calls always use explicit UTF-8 decoding with replacement semantics.
_web_ui_build_needed() in PR #14914 checked web_dir/"dist" as the
sentinel, but vite.config.ts sets outDir: "../hermes_cli/web_dist" so
the build output lands in hermes_cli/web_dist/, never in web/dist/.
The sentinel was therefore always missing → _web_ui_build_needed always
returned True → npm install + Vite build ran on every startup → OOM on
low-memory VPS persisted unchanged.
Fix: derive dist_dir as web_dir.parent / "hermes_cli" / "web_dist" so
the sentinel points to the actual build output directory.
Fixes#14898
